The present invention relates to heaters used to dispense air treatment chemicals, such as insect control agents, fragrances and deodorizers. More particularly, it relates to structures incorporated into such heaters for more efficiently spreading the heat generated by a heating element to a dispensing wick.
One known type of air treatment chemical dispenser is that disclosed in U.S. patent application publication 2009/0196586, the disclosure of which is incorporated by reference. In this dispenser a liquid air treatment chemical is stored in a bottle. A wick extends into the liquid, and then projects upward out of the bottle. The upward end of the wick is surrounded by a ring-type electrical heater. Heating of a ring causes air treatment chemical to be driven from the wick to the surrounding environment.
In this 2009/0196586 device the heat is generated by a positive temperature coefficient heating element in the form of a pill-shaped tablet formed from pressed conductive granular material. Its resistivity to electrical charge generates heat, and that resistivity decreases with an increase in temperature, thereby providing an inherent desirable control function against overheating.
This product had a two-part outer housing for the heater. When assembled they formed an enclosure that was generally doughnut shaped, but hollow. There were two generally arc-shaped electrical contacts positioned in the housing to extend around a central axial through bore, the bore being sized to receive the wick. One end of one contact connected to one prong of an external plug. At the other end of that contact there was a platform designed to contact a positive temperature coefficient type pill heating element.
On the other side of the heater was placed a second arc-shaped electrical contact that also extended around the through bore. It had a connection to another plug prong at one end, and another surface at an opposed end designed to rest against an opposed side of the positive temperature coefficient pill. A spring was included to help the contacts stay in close abutment with the heater even when thermal expansion of the assembly occurred during use.
Electrical charge passed through the contacts to the heater pill, causing the pill to generate heat. The generated heat was then carried back along the contact to spread the heat around the through bore, and then to the wick. Heating of the wick facilitated volatilization of air treatment chemicals drawn up by the wick.
There was also a cylindrical extension from one outer housing part. It was surrounded by axial arc extensions integral with the electrical contacts. While these arc extensions helped improve thermal heat transfer to the wick somewhat, they added complexity and cost to the manufacture of the contacts, required some compromises in the design of the contacts, and in any event did not fully optimize energy use.
U.S. Pat. No. 6,411,776 disclosed another heater where upstanding portions of the contacts surrounded a cylindrical extension from an outer housing. While integrated axial extensions on electrodes completely surrounded the cylindrical extension from the outer housing in this device, there were still similar problems in using this type of construction (e.g. complexity; cost; material compromises; energy inefficiency).
See also U.S. Pat. No. 5,940,577 where contact elements were provided with integrated cylindrical extensions.
U.S. Pat. No. 4,874,924 disclosed another heating device where an outer housing was provided with a cylindrical extension passing through the electrical contacts. However, here an internal sleeve was positioned radially inward of the cylindrical extension. Again, in this device there were significant heat transfer inefficiencies. Further, having the sleeve partially exposed outside the housing presented other concerns.
See also CN 2281074 for an approach analogous to that used in U.S. Pat. No. 4,874,924. Similarly, there is a commercially available All-out heater of this type.
Hence, a need still exists for improved heaters for use with wick-type volatile liquid dispensers.